/*
 * Copyright 2012-2016 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.boot.web.servlet;

import org.springframework.util.Assert;
import org.springframework.util.ObjectUtils;

import javax.servlet.MultipartConfigElement;
import javax.servlet.Servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRegistration;
import javax.servlet.ServletRegistration.Dynamic;
import java.util.Arrays;
import java.util.Collection;
import java.util.LinkedHashSet;
import java.util.Set;

/**
 * A {@link ServletContextInitializer} to register {@link Servlet}s in a Servlet 3.0+
 * container. Similar to the {@link ServletContext#addServlet(String, Servlet)
 * registration} features provided by {@link ServletContext} but with a Spring Bean
 * friendly design.
 * <p>
 * The {@link #setServlet(Servlet) servlet} must be specified before calling
 * {@link #onStartup}. URL mapping can be configured used {@link #setUrlMappings} or
 * omitted when mapping to '/*' (unless
 * {@link #ServletRegistrationBean(Servlet, boolean, String...) alwaysMapUrl} is set to
 * {@code false}). The servlet name will be deduced if not specified.
 *
 * @author Phillip Webb
 * @see ServletContextInitializer
 * @see ServletContext#addServlet(String, Servlet)
 * @since 1.4.0
 */
public class ServletRegistrationBean extends RegistrationBean
{

    private static final String[] DEFAULT_MAPPINGS = {"/*"};

    private Servlet servlet;

    private Set<String> urlMappings = new LinkedHashSet<String>();

    private boolean alwaysMapUrl = true;

    private int loadOnStartup = -1;

    private MultipartConfigElement multipartConfig;

    /**
     * Create a new {@link ServletRegistrationBean} instance.
     */
    public ServletRegistrationBean()
    {
    }

    /**
     * Create a new {@link ServletRegistrationBean} instance with the specified
     * {@link Servlet} and URL mappings.
     *
     * @param servlet     the servlet being mapped
     * @param urlMappings the URLs being mapped
     */
    public ServletRegistrationBean(Servlet servlet, String... urlMappings)
    {
        this(servlet, true, urlMappings);
    }

    /**
     * Create a new {@link ServletRegistrationBean} instance with the specified
     * {@link Servlet} and URL mappings.
     *
     * @param servlet      the servlet being mapped
     * @param alwaysMapUrl if omitted URL mappings should be replaced with '/*'
     * @param urlMappings  the URLs being mapped
     */
    public ServletRegistrationBean(Servlet servlet, boolean alwaysMapUrl, String... urlMappings)
    {
        Assert.notNull(servlet, "Servlet must not be null");
        Assert.notNull(urlMappings, "UrlMappings must not be null");
        this.servlet = servlet;
        this.alwaysMapUrl = alwaysMapUrl;
        this.urlMappings.addAll(Arrays.asList(urlMappings));
    }

    /**
     * Returns the servlet being registered.
     *
     * @return the servlet
     */
    protected Servlet getServlet()
    {
        return this.servlet;
    }

    /**
     * Sets the servlet to be registered.
     *
     * @param servlet the servlet
     */
    public void setServlet(Servlet servlet)
    {
        Assert.notNull(servlet, "Servlet must not be null");
        this.servlet = servlet;
    }

    /**
     * Set the URL mappings for the servlet. If not specified the mapping will default to
     * '/'. This will replace any previously specified mappings.
     *
     * @param urlMappings the mappings to set
     * @see #addUrlMappings(String...)
     */
    public void setUrlMappings(Collection<String> urlMappings)
    {
        Assert.notNull(urlMappings, "UrlMappings must not be null");
        this.urlMappings = new LinkedHashSet<String>(urlMappings);
    }

    /**
     * Return a mutable collection of the URL mappings for the servlet.
     *
     * @return the urlMappings
     */
    public Collection<String> getUrlMappings()
    {
        return this.urlMappings;
    }

    /**
     * Add URL mappings for the servlet.
     *
     * @param urlMappings the mappings to add
     * @see #setUrlMappings(Collection)
     */
    public void addUrlMappings(String... urlMappings)
    {
        Assert.notNull(urlMappings, "UrlMappings must not be null");
        this.urlMappings.addAll(Arrays.asList(urlMappings));
    }

    /**
     * Sets the {@code loadOnStartup} priority. See
     * {@link ServletRegistration.Dynamic#setLoadOnStartup} for details.
     *
     * @param loadOnStartup if load on startup is enabled
     */
    public void setLoadOnStartup(int loadOnStartup)
    {
        this.loadOnStartup = loadOnStartup;
    }

    /**
     * Set the {@link MultipartConfigElement multi-part configuration}.
     *
     * @param multipartConfig the multi-part configuration to set or {@code null}
     */
    public void setMultipartConfig(MultipartConfigElement multipartConfig)
    {
        this.multipartConfig = multipartConfig;
    }

    /**
     * Returns the {@link MultipartConfigElement multi-part configuration} to be applied
     * or {@code null}.
     *
     * @return the multipart config
     */
    public MultipartConfigElement getMultipartConfig()
    {
        return this.multipartConfig;
    }

    /**
     * Returns the servlet name that will be registered.
     *
     * @return the servlet name
     */
    public String getServletName()
    {
        return getOrDeduceName(this.servlet);
    }

    @Override
    public void onStartup(ServletContext servletContext) throws ServletException
    {
        Assert.notNull(this.servlet, "Servlet must not be null");
        String name = getServletName();
        if (!isEnabled())
        {
            return;
        }
        Dynamic added = servletContext.addServlet(name, this.servlet);
        if (added == null)
        {
            return;
        }
        configure(added);
    }

    /**
     * Configure registration settings. Subclasses can override this method to perform
     * additional configuration if required.
     *
     * @param registration the registration
     */
    protected void configure(ServletRegistration.Dynamic registration)
    {
        super.configure(registration);
        String[] urlMapping = this.urlMappings.toArray(new String[this.urlMappings.size()]);
        if (urlMapping.length == 0 && this.alwaysMapUrl)
        {
            urlMapping = DEFAULT_MAPPINGS;
        }
        if (!ObjectUtils.isEmpty(urlMapping))
        {
            registration.addMapping(urlMapping);
        }
        registration.setLoadOnStartup(this.loadOnStartup);
        if (this.multipartConfig != null)
        {
            registration.setMultipartConfig(this.multipartConfig);
        }
    }

}
